Sc Zr Alloy Research Articles

Effect of laser parameters on microstructure and mechanical properties of Al–Ni–Sc–Zr alloys fabricated by laser powder bed fusion

The processability, microstructure and mechanical properties of a near eutectic AlNiScZr alloy fabricated by laser powder bed fusion (LPBF) are investigated. The optimal processing windows for the LPBF alloy are determined. The results indicate that laser power exerts a predominant influence on the relative density of the as-built alloy. Elevated laser power can lead to increased relative density. Laser scanning speed exerts a significant impact on the microstructure and mechanical properties of the as-built alloys. An increase in the laser scanning speed can facilitate the growth of coarse columnar grains in the coarse grain region and suppress the formation of ultrafine equiaxed grain bands. Furthermore, the increase in the laser scanning speed can result in a reduction in the size of the cells, which in turn leads to an enhancement in the strength of the alloys. This study examines the evolution of the microstructure and mechanical properties of the as-built alloy as a function of laser scanning speed. By elucidating the relationship between laser parameters, microstructure and mechanical properties, the objective is to provide fundamental guidance for tuning the solidification structures and mechanical properties of LPBF AlNiScZr alloys by selecting appropriate laser parameters.

Anisotropic microstructure and tensile property of laser powder bed fusion fabricated Al–Mn–Mg–Sc–Zr alloy built at different layer thickness

Laser powder bed fusion (LPBF) fabricated Al–Mn–Mg-Sc-Zr alloy generally possesses a bi-modal microstructure of columnar grains and equiaxed grains. Such an anisotropic microstructure would introduce varied tensile performance in different orientations. To date, few study on the microstructure and tensile property anisotropy have been reported for LPBF fabricated Al–Mn–Mg-Sc-Zr alloys built at different layer thicknesses, which limits the exploration in mechanical property optimization. In this work, the microstructure anisotropy and room-temperature tensile properties of LPBF produced and peak-aged Al–Mn–Mg-Sc-Zr alloys built at 30 and 60 μm layer thicknesses were systematically investigated by scanning electron microscope, transmission electron microscope, and tensile testing. A higher layer thickness of 60 μm resulted in coarser grains with the precipitates size remained similarly compared to the 30 μm specimens. This led to a reduced yield strength in 60 μm specimens (492–509 MPa) comparing to those in 30 μm specimens at 502 MPa–510 MPa. In addition, the existence of columnar grains within melt pools contributed to a larger effective slip length in the vertical direction than that in the horizontal orientation. Such difference in effective slip length in the loading direction contributed to a lower strength in vertical orientations. For ductility, the slightly higher defect level in 60 μm specimens (0.58%) resulted in reduced elongations of 3%–6% compared to those of 30 μm specimens (0.10%). The ductility anisotropy was attributed to the preferential distribution of gas pores and keyhole defects at melt pool boundaries.

Improved elevated-temperature strength and thermal stability of additive manufactured Al–Ni–Sc–Zr alloys reinforced by cellular structures

Laser powder bed fusion (LPBF) processed Al–Ni alloys typically exhibit cellular structures, contributing to superior strength at ambient temperature as the cell walls can effectively impede dislocation motion during plastic deformation. However, it is still unclear whether cellular structures can lead to excellent elevated-temperature performance. In this study, we conducted a systematic investigation into the elevated-temperature mechanical properties and thermal stability of an LPBF Al–Ni–Sc–Zr alloy with cellular structures. The as-built alloy exhibits a yield strength of 368 MPa at 25℃ and 332 MPa at 250℃, with an exceptional strength retention rate of ∼90 % at 250℃. Moreover, the alloy maintains a hardness of ∼146 HV following exposure at 250℃ for 100 h and shows no apparent decrease despite increasing the exposure time to 500 h. The excellent elevated-temperature performance can be attributed to the cellular structures. The cell walls effectively confine dislocations at elevated temperatures, suppressing the dislocation annihilation and leading to exceptional strength retention. On the other hand, even if the cell walls decompose into nanoparticles after prolonged thermal exposure, the reduction in strength due to the decomposition can be compensated by the strengthening of the nanoparticles, resulting in excellent thermal stability. By studying the influence of the cellular structures on elevated-temperature performance, this study could provide valuable insights into developing high-performance Al alloys for elevated-temperature applications by additive manufacturing.

Parameter study of an Al–Cr–Mo–Sc–Zr alloy processed by laser powder bed fusion reaching high build rates

Parameter study of an Al–Cr–Mo–Sc–Zr alloy processed by laser powder bed fusion reaching high build rates

Approaching 1 GPa Ultra‐High Tensile Strength in a Nanostructured Al–Zn–Mg–Cu–Zr–Sc Alloy Prepared by Severe Plastic Deformation

Alloy composition and heat treatment processes have limited possibility to enhance ultra‐high strength of aluminum alloys, which restricts their widespread application in lightweight equipment. Consequently, high‐density dislocations and grain refinement are suggested to strengthen ultra‐high strength aluminum alloys. Herein, a novel nanostructured Al–Zn–Mg–Cu–Zr–Sc (AZMCZS) alloy with homogeneous microstructure is prepared through the synergistic processing of hot extrusion and high‐pressure torsion. Additionally, the microstructures and strengthening mechanisms of the nanostructured Al alloy are analyzed. It is observed that the ultimate tensile strength of the nanostructured Al alloy reaches nearly 1 GPa, and the elongation of the alloy is 1.9%. The nanostructured Al alloy mainly consists of nanoscale grains (≈117.7 nm), high‐density dislocations (2.4 × 1015 m−2), nano‐sized precipitates (the size of 20–51 nm), and solute atom clusters (≈3 nm). The multiple strengthening mechanisms of the nanostructured Al alloy are revealed in terms of grain refinement, dislocations, precipitates, and solute atom clusters. Grain refinement and dislocation strengthening show superior outcomes and are considered to be the predominant strengthening mechanisms. These findings demonstrate that this nanostructural architecture offers a new way to design super‐strength metals and alloys by effectively controlling the processing regime of severe plastic deformation.

Microstructure evolution and mechanical properties of high-performance Al–Mn–Mg–Sc–Zr alloy fabricated by laser powder bed fusion

The influence of aging temperatures on the microstructure and mechanical properties of an Al–Mn–Mg– Sc–Zr alloy prepared by laser powder bed fusion (L-PBF) was systematically studied. The results show that the fabricated alloy was a dense and crack-free piece with a fine grain size of 3.51 μm and a yield strength of (547±3) MPa. When the alloy was subjected to aging at 300 °C, a large amount of highly coherent Al3Sc nanoparticles (2–3 nm) precipitated from the Al matrix. The aged sample exhibited a high yield strength of (616±4) MPa, which can be attributed to precipitation strengthening, solid solution strengthening, and grain boundary strengthening. When the alloy was aged at a temperature higher than 300 °C, part of the dissolved Mn and Zr precipitated in the form of Al6Mn and Al3(Sc,Zr). When the alloy was aged at 500 °C, the Al6Mn and Al3(Sc,Zr) precipitates grew to approximately 600 and 30 nm, respectively, in size. Consequently, the yield strength of the alloy decreased to (372±3) MPa.

Microstructure evolution and strengthening mechanisms of a high-performance TiN-reinforced Al–Mn–Mg–Sc–Zr alloy processed by laser powder bed fusion

In this work, a high-strength crack-free TiN/Al–Mn–Mg–Sc–Zr composite was fabricated by laser powder bed fusion (L-PBF). A large amount of uniformly distributed L12-Al3(Ti, Sc, Zr) nanoparticles were formed during the L-PBF process due to the partial melting and decomposition of TiN nanoparticles under a high temperature. These L12–Al3(Ti, Sc, Zr) nanoparticles exhibited a highly coherent lattice relationship with the Al matrix. All the prepared TiN/Al–Mn–Mg–Sc–Zr composite samples exhibit ultrafine grain microstructure. In addition, the as-built composite containing 1.5 wt% TiN shows an excellent tensile property with a yield strength of over 580 MPa and an elongation of over 8 %, which were much higher than those of wrought 7xxx alloys. The effects of various strengthening mechanisms were quantitatively estimated and the high strength of the alloy was mainly attributed to the refined microstructure, solid solution strengthening, and precipitation strengthening contributed by L12–Al3(Ti, Sc, Zr) nanoparticles.

Effect of Sc contents on the mechanical properties and damping capacity of Al–Zn–Mg–Cu–Zr–Sc alloys with different grain structures

Al–Zn–Mg–Cu–Zr–Sc alloys with different Sc contents were fabricated by casting, deformation, and T6 treatment. Deformation methods including rolling and friction-stir processing (FSP) were used to design their grain structure. A low additive amount (0.1) of Sc cannot refine the grains of the alloy with rolling and T6 treatment, and it instead coarsened the grains. The reason was the non-uniform distribution of nanosize Al3(Sc,Zr) phases that led to the occurrence of abnormal grain growth during homogenization. Meanwhile, the alloy with only 0.1Sc exhibited finer grains after FSP and T6 treatment than the alloys subjected to the same process but with higher Sc additive amount. Alloys with rolling-induced elongated grain structure exhibited better mechanical properties, and alloys with FSP-induced fine equiaxed grain structure exhibited higher high-strain and high-temperature internal friction values. These features are important performance parameters for applications in fields where vibration and noise are sensitive. The optimum additive amounts of Sc for alloys with elongated and fine equiaxed grain structures were 0.25 and 0.1, respectively.

Simultaneously Improving Strength and Plasticity of Al–Cu Alloy by Introducing Spherical Precipitates

The trade‐off relation between strength and plasticity is the bottleneck that limits the development of high‐strength and high‐plasticity Al–Cu alloys. Inspired from the influence of precipitate shape on the work‐hardening behavior of Al–Cu alloys, an Al–Cu–Zr–Sc alloy containing a mixed microstructure of spherical‐shaped Al3(Zr, Sc) phases and disk‐shaped θ′ phases is successfully designed and fabricated. Surprisingly, it is found that the strength and plasticity of the Al–Cu–Zr–Sc alloy are synchronously improved compared to the Al–Cu alloy with only disk‐shaped θ′ phases. The introduction of spherical‐shaped Al3(Zr, Sc) phases can increase the yield strength without sacrificing the work‐hardening ability of the Al–Cu–Zr–Sc alloy, which is mainly attributed to the extremely small strain‐hardening exponent of the Al alloy with spherical‐shaped precipitates. Besides, the predicted strength–elongation relation of the Al–Cu alloy is established based on the exponential strain‐hardening model.

Anisotropic tensile creep behavior in laser powder bed fusion manufactured Al–Mn–Mg–Sc–Zr alloy

The recently emerged Al–Mn–Mg–Sc–Zr alloys were regarded as high-strength Al alloys suitable for high-temperature applications. However, the influence of laser powder bed fusion (LPBF) fabricated anisotropic microstructure on tensile creep performance has not been explored. In this work, we reported an anisotropic tensile creep behavior, which is superior in the vertical specimens than the horizontal counterparts. The tensile creep anisotropy was attributed to the bi-modal microstructure of columnar grains within melt pool and equiaxed grains at melt pool boundary, the “fish-scale” melt pool morphology and the resulted tortuous crack path in the vertical orientation.

Microstructure and mechanical properties of a novel Al–Mg–Er–Zr-Sc alloy fabricated by selective laser melting

In this work, Er–Zr-Sc modified Al–Mg alloy, manufactured by selective laser melting, offers excellent mechanical properties, due to the formation of a desirable microstructure and the synergistic effects of multiple strengthening mechanisms. The microstructure in as-built and aged alloys have been characterized by scanning electron microscopy and transmission electron microscopy. The results show that the microstructure of alloy is composed of equiaxed grains (∼0.7 μm in diameter) along the boundary of molten pool and columnar grains (∼1.46 μm in width) inside the molten pool. Al3(Sc,Zr) particles serve as nucleation sites to promote the nucleation of equiaxed grains, and Al3(Er,M) eutectic phases and other compounds at the grain boundaries inhibit grain growth, both of which greatly refine the grains and bring significant grain boundary strengthening and Orowan strengthening effect. During the aging process, coherent Al3(Er,Zr,Sc) nano-precipitates are dispersedly precipitated from the Al matrix, which plays a key role in improving the mechanical properties of the aged alloy, and then the alloy reaches a yield strength of 530 MPa, a tensile strength of up to 542 MPa, and an elongation of over 12 %. Under the combined addition of Er, Sc, and Zr, and the influence of multi-element interaction, the alloy has high-density secondary phases and extremely fine grains, which are the main sources of reinforcement.

The Dynamic Recrystallization in a Hot‐Compressed Al–Zn–Mg–Cu–Sc–Zr Alloy: The Role of Strain Rate

The effects of strain rates (0.001–1 s−1) on the microstructures and mechanical performance of the novel Al–Zn–Mg–Cu alloy through hot compression at 300 °C are investigated in detail. With the increase of strain rate, the dislocation density increases from 0.06 × 1013 to 3.77 × 1013 m−2, which promotes the dynamic precipitation kinetics. And the volume fraction of η precipitates is calculated by the differential scanning calorimetry curves increasing from 1.36% to 3.94%. Both dislocations and precipitates promote to increase the hardness of the Al–Zn–Mg–Cu alloy. The large number of η precipitates in high‐strain‐rate samples hinders the recrystallization process by impeding the movement of dislocations and grain boundaries, decreasing the volume fraction of recrystallized grains to 3.1%. Continuous/discontinuous dynamic recrystallization occurs preferentially at low strain rates, and discontinuous dynamic recrystallization is rarely observed in high‐strain‐rate samples. In addition, because the process of continuous dynamic recrystallization promotes the transformation from low‐angle grain boundaries to high‐angle grain boundaries, more continuous dynamic recrystallized grains and less low‐angle grain boundaries can be observed in low‐strain‐rate samples.

Strong and ductile Al–Mn–Mg–Sc–Zr alloy achieved in fabrication-rate enhanced laser powder bed fusion

ABSTRACT The high cost of laser powder bed fusion (LPBF) fabricated high-strength Sc containing aluminium alloy hinders its applications. To reduce the cost, we reported a LPBF fabricated strong and ductile Al–Mn–Mg–Sc–Zr alloy using large layer thicknesses to improve the fabrication efficiency on coarse powder particles. A high relative density exceeding 99.2% was achieved at layer thicknesses up to 120 μm. In post-process heat-treated specimens, the yield strength only had a slight 6% decrease from layer thickness of 30 to 120 μm; such a decrease in strength was attributed to the larger grain size resulted from the adopted larger layer thickness. The fabricated sample at layer thickness of 120 μm still exhibited high tensile yield strength of 472 MPa and fracture strain of ∼10%. This work showed a successful application of improving the LPBF fabrication efficiency of high-strength Al–Mn–Mg–Sc–Zr alloy using large layer thickness in LPBF process.

Synergic effects of Si and V micro-additions on microstructural and mechanical properties of a dilute Al–Sc–Zr alloy containing L12 Al3(Sc, Zr, V) nanoprecipitates

This study investigates the impact of incorporating 0, 0.05, 0.10 at% V into a bare Al-0.06Sc-0.06Zr-0.18Si at% alloy on the precipitation behavior of Al3(Sc, Zr, V) (L12-structure) nanoprecipitates and the consequent creep resistance of the alloy. Various techniques were used to obtain results, including Vickers microhardness, Electrical conductivity, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and tensile creep rupture testing. The findings show that the amount of V added affected the nanoprecipitate structures, precipitation kinetics, coarsening resistance, and creep resistance of the alloys. After isochronal aging to 425 °C (25 °C/1 h step), alloy V0.10 had a peak microhardness value of 603 ± 14 MPa. TEM revealed a microstructure with precipitate diameters ranging from 3 to 20 nm. The nanoprecipitates had a core-shell structure with a Sc-enriched core, a Zr-enriched shell, and, in some cases, a V outer shell. The phenomenon of vanadium partitioning at the precipitate shells occurred due to the incremental influence of silicon, which enhanced the diffusion rate of Zr and V. While the alloy V0.10 had a lower steady-state strain rate than the Al-0.06Sc-0.06Zr at% alloy at stresses below 16 MPa, it showed better creep resistance at stresses above 16 MPa. The threshold stress of the alloy V0.10 (10 MPa) was almost equal to that of the previously studied Al-0.06Sc-0.06Zr at% alloy (12 MPa). These results can be explained by the fact that a variation in the lattice parameter of Al3(Sc, Zr, V) (L12) affects the ability of matrix dislocations to traverse the nanoprecipitates, even in the absence of measurable lanthanides.

Microstructure, mechanical properties, and damping capacity of high-Zn-content Al–Zn–Mg alloys with Sc and Zr additions

In this study, Al–15Zn–0.5 Mg–Sc–Zr alloys with different Sc and Zr contents were fabricated by casting, rolling, solution treatment, and aging at low and high temperatures. Primary and precipitated Al3(Sc,Zr) and Al3Zr phases could promote grain refinement in the high-Zn-content Al alloys more effectively than the Al3Sc phase, and the composition characteristics of high Zn and low Mg contents led to the Al–15Zn–0.5 Mg–Sc–Zr alloys exhibiting high thermal stability of η′ phases during aging at high temperature and long time. The Al3Sc and Al3(Sc,Zr) phases could promote the formation of fine η phases in the Al–15Zn–0.5 Mg–Sc–Zr alloys, but the Al3Zr phase could not. Finer grains and second phases led to the Al–15Zn–0.5 Mg–Sc–Zr alloys with Zr single addition and Sc, Zr collaborative additions exhibiting better mechanical properties than the alloy with Sc single addition. Meanwhile, the damping capacities of the Al–15Zn–0.5 Mg–Sc–Zr alloys with high-temperature aging were higher than those of the same alloys with aging at a low temperature due to their less numbers of dislocation pinning points and higher interface slipping ability.

Co-segregation effect of Si and Zr at Al/L12–Al3Sc interface

Reducing the usage of Sc element, as well as improving the thermal stability of nano-precipitate L12–Al3Sc are critical in expanding the application field of Al–Sc based alloys. Previous experiments showed that the impurity Si plays a leading role in accelerating the precipitation and strengthening the thermal stability of Al–Sc-Zr alloy, but the micro mechanism of these effects are not be given at atomic and electron scale. Herein, we performed a first-principles calculations to focus on the segregation behaviors of Si and Zr at Al (001)/L12-Al3Sc (001) interface. The results show that the ahead segregated Si atom, which prefers to occupy the Al site of Al3Sc precipitate side, contributes to induce Zr substituting the Sc atom that is the nearest neighbor of Si rather than the Sc site in Al matrix side. A quantitative calculation suggests that the reduction of Sc usage can at least reach 12 % as the concentration of added Si in Al bulk is about 0.06 %.

High Cycle Fatigue Property of Al–Mg–Sc–Zr Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) of high‐strength Al–Mg–Sc–Zr alloy possesses great potential application in the aerospace industry. However, fatigue performance has become a very important issue in the safety and durability design of engineering structures. Herein, the high cycle fatigue property of LPBF‐fabricated Al–Mg–Sc–Zr alloy and its correlation with defects, microstructure, and precipitated phases are studied. The LPBF‐manufactured Al–Mg–Sc–Zr alloy appears heterogeneous structure composed of equiaxed grains at the molten pool boundary and columnar grains at the inner of the molten pool. After aging treatment (325 °C/4 h), the nanosized Al3Sc intragranular particles and Mn‐rich intergranular particles are precipitated, leading to more difficult movement of dislocations that favors the fatigue strength. The ultimate tensile strength of the samples after aging treatment is 507.05 MPa and corresponding 107 cycle fatigue strength (R = −1) is 106 MPa. The fracture morphology of the fatigue specimens shows that the fatigue cracks start from the surface defects with strong stress concentration, especially the lack of fusions, and then expand through the surplus part.

The Microstructure and Mechanical Properties of Al–Mg–Fe–Ni–Zr–Sc Alloy after Isothermal Multidirectional Forging

The Microstructure and Mechanical Properties of Al–Mg–Fe–Ni–Zr–Sc Alloy after Isothermal Multidirectional Forging

An additively manufactured heat-resistant Al-Ce-Sc-Zr alloy: Microstructure, mechanical properties and thermal stability

In this study, a high-strength and heat-resistant Al–Ce–Sc–Zr alloy was designed and fabricated by additive manufacturing. The as-built alloy shows an excellent combination of strength and ductility compared to other Al–Ce-based alloys, including an ultimate tensile strength of 445 MPa, a yield strength of 344 MPa and an elongation of 10%. Even at 300 °C, the alloy still retains a superb tensile yield strength of 233 MPa, which is the best among the high-temperature aluminum alloys reported so far. The excellent performance is mainly attributed to a significant amount of fine, homogeneous and coarsening-resistant Al11Ce3 intermetallic nanoparticles formed during the rapid solidification process of laser additive manufacturing. The formation of coherent Al3(Sc, Zr) nano-precipitates and interfacial segregation at the interface of intermetallic nanoparticles during high temperature exposure further improve the high temperature properties of the alloy. Our work has the potential to provide design concepts for the development of novel high temperature aluminum alloys.

Fracture toughness and high-cycle fatigue behaviour of Al–Mg and Al–Mg–Sc–Zr alloys

Tensile, fracture toughness and high-cycle fatigue tests were carried out on Al–Mg and Al–Mg–Sc–Zr alloys. Fracture morphology and the microstructure of the alloys were observed by SEM and TEM, etc. Al–Mg–Sc–Zr alloy with fibrous fine grain structure showed higher tensile strength and fracture toughness than Al–Mg alloy, which had a larger grain size and obvious recrystallisation. In high-cycle fatigue tests, Al–Mg–Sc–Zr alloy presented a higher fatigue limit owing to its finer grains and nanosized precipitates, which increased the difficulty of fatigue crack initiation. Al–Mg alloy presented a lower fatigue limit because crack initiation caused by slip is more likely to occur. However, its rougher fracture surfaces may be beneficial to hindering the propagation of macrocracks.